In many gas turbine engines, a low pressure spool includes a low pressure turbine that is connected to and drives a low pressure compressor, and a high pressure spool includes a high pressure turbine that is connected to and drives a high pressure compressor. In certain configurations, the low pressure spool drives a fan via a geared architecture. A lubrication system includes a main pump that is driven by the high pressure spool to pump lubricating and cooling liquid to engine components as needed.
Some gas turbine engines include a windmill emergency oil system to protect the fan drive gear system under low or no oil conditions. For example, when the high pressure spool stops rotating or rotates at a reduced rpm (revolutions per minute), the fan drive gear system can continue rotating even though the main pump will ordinarily provide little or no liquid during this time. Such a situation can arise when the wind rotates the fan and corresponding gears and bearings while the aircraft is parked on the ground, or during an in-flight engine shutdown. The windmill emergency oil system operates to protect gears and bearings from damage during the relatively short periods of non-lubricated operation.
Over time, these lubrication systems can become clogged with debris. In certain applications a filter has been installed to protect bearings within the fan drive system from debris. One problem with existing filters is that the filter permanently traps debris such that the debris remains in place until the fan drive gear system is overhauled. Further, in one known configuration, the filter is located within the fan drive gear system bearing journals such that the entire engine needs to be disassembled to remove and change the filter. Another problem with existing systems is that upon engine start-up and shut-down, the windmill system can send un-filtered lubrication to the journal bearings, which further clogs the filters with debris over time.